Hadley's Quadrant

Though the first sextants were built by the 1790s, most navigators were still used a Hadley's Quadrant, or Octant, up into the middle of the 19th century. The quadrant's legs subtended a 45 degree angle, but with the double reflecting system enabled measurement of angles up to 90 degrees. The sextant could measure angles up to 120 degrees.

This image is from a navigation book written by John Hamilton Moore called The New Practical Navigator.... published in London in 1796, the 12th edition of his work first published as The practical navigator, and seaman's daily assistant.